Aliexpress
Click here… to search for Xiaomi TOSWIM Plus Size Silicone Swimming Cap on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is one coupon right now! Check this out.
Link: Banggood product page
Coupon (19.79 USD): BG10OFFAFF1
(CouponsFromChina.com tip: you should apply the coupon in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): TTxBG10, BGOD1, 2019SPEDM, AFfbG10, 13f142, BGMPB2020, BGAFF10OFF, bGhOnEy10, BGdragonBoat, BGSS10%SW, bgshOOp10, BgoFErTaSchInA10, BgcLuBofErtA10, BGCuponation10, BGHONEY2110, BG10OFFAFF, BGwhielabel
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Here is price history (for all/most countries) for Xiaomi TOSWIM Plus Size Silicone Swimming Cap.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).